The invention relates to panel displays, and more particularly, to systems and methods for providing driving voltages to RGBW display panels.
Color image display devices are well known and are based upon a variety of technologies such as cathode ray tubes, liquid crystal modulators and solid-state light emitters such as Organic Light Emitting Diodes (OLEDs). In a common OLED color image display device, a pixel includes red, green and blue colored subpixels. These light emitting colored subpixels define a color gamut, and by additively combining the illumination from each of these three subpixels, i.e. with the integrative capabilities of the human visual system, a wide variety of colors can be achieved. OLEDs may be used to generate color directly using organic materials to emit energy in desired portions of the electromagnetic spectrum, or alternatively, broadband emitting (apparently white) OLEDs may be attenuated with color filters to achieve red, green and blue output.
Images and data displayed on a color display device are typically stored and/or transmitted in three channels, that is, having these signals corresponding to a standard (e.g. RGB). It is also important to recognize that data typically is sampled to assume a particular spatial arrangement of light emitting elements. In an OLED display device, these light emitting elements are typically arranged side by side on a plane. Therefore, if incoming data is sampled for display on a color display device, the data will also be resampled for display on an OLED display having four subpixels per pixel rather than the three subpixels used in a three channel display device.
In this regard, FIG. 1A shows a conventional OLED subpixel driving circuit structure, and FIG. 1B shows RGBW subpixel arrangements of a conventional display panel. As shown in FIG. 1A, the subpixel is driven by the current I1 through the driving transistor T1. The driving transistor T1 outputs the current I1 according to the voltage V1.
FIG. 1C shows a conventional digital signal processing (DSP) structure for driving RGBW subpixels. As shown in FIG. 1C, RGB digital signals are sampled and held and output to a Gamma linear control unit. The Gamma linear control unit adjusts RGB digital signals for Gamma linearity and outputs to the conversion unit. The conversion unit converts the adjusted RGB digital signals to RGBW digital signals and outputs to a Gamma compensation unit. The Gamma compensation unit executes a Gamma compensation of the RGBW digital signals from the conversion unit for Gamma correction and outputs to a RGBW driver. The RGBW driver converts the RGBW digital signals to RGBW analog signals to drive corresponding RGBW subpixels.
FIG. 2A shows the relationship between the luminance of the OLED subpixel and the current I1. As shown, there is a linear relationship between the luminance of the OLED subpixel and the current I1. FIG. 2B shows the relationship between the current I1 of the driving transistor T1 and the voltage V1 to be non-linear. FIG. 2C shows the relationship between luminance of the OLED subpixel and observable brightness (gamma). FIG. 2D shows the relationship between observable brightness and voltage V1 applied to the driving transistor T1.
Thus, a gamma correction is required to compensate the non-linear relationship.
Conventionally, RGB data is converted to RGBW data through digital data processing (DSP). However, due to different optical characteristics (gamma correction) for each RGBW color, DSP typically requires a complicated algorithm to execute such conversion. Further, it may be difficult to obtain a precise analog output corresponding to the gamma correction for each color after using the complicated conversion algorithm.
For example, FIG. 3 shows a conventional method for converting RGB data to RGBW data. As shown in FIG. 3, the Min(R,G,B) is assumed to be W data, and R′G′B′ data (driving the display device) can be obtained by removing the W component from the R,G,B components respectively. FIG. 4 shows another conventional method for converting RGB data to RGBW data. As shown in FIG. 4, the Min(R,G,B) is assumed to be W data, and the W component is converted to W′ data in accordance with a characteristic of α*W, where α<1. The R′G′B′ data are obtained by removing the W′ component from the RGB components respectively. However, these two simple methods typically cannot precisely provide gamma correction for each color because of the non-linear relationship between driving voltage and observable brightness.